消化与吸收Digestion and Absorption

夏 强， PhD浙江大学医学院生理学系医学院科研楼 C 座 518 室

电话： 88208252Email ： xiaqiang@zju.edu.cn

两个概念• 消化——是指食物中所含的营养物质在消

化道内被分解为可吸收的小分子物质的过程– 机械性消化– 化学性消化

• 吸收——食物经消化后形成的小分子物质，以及维生素、无机盐和水通过消化道黏膜上皮细胞进入血液和淋巴的过程

• 消化系统• 消化道• 消化腺

消化系统的功能• 运动 Movement• 分泌 Secretion• 消化 Digestion• 吸收 Absorption• 排出 Elimination

Structure of the alimentary canal

Normal BER frequencies in the gastrointestinal system

基本电节律 basic electrical rhythm: BER

两套神经系统• 肠（内在）神经系统 Enteric nervous system (intrinsic)• 自主（外来）神经系统 Autonomic nervous system (extrinsic)

胃肠激素Gastrointestinal hormones

• 消化道内所含的内分泌细胞数远大于体内所有内分泌腺所含的细胞总数

• 消化道是目前所知的体内最大的内分泌器官

• Gastrointestinal hormones ， Gut hormones

口腔内消化

咀嚼和吞咽Mastication and swallowing

The swallowing reflex is coordinated by the medulla oblongata, which stimulates the appropriate sequence of contraction and relaxation in the participating skeletal muscle, sphincters, and smooth muscle groups.

The coordinated sequence of contraction and relaxation in the upper esophageal sphincter, the esophagus, and the lower esophageal sphincter is necessary to deliver swallowed food to the stomach.

胃内消化• 胃的主要功能：

– 暂时储存食物– 消化食物– 少量吸收

• 胃液 Gastric juice 成分– HCl– 胃蛋白酶原 Pepsinogen– 黏液 Mucus– 碳酸氢盐 HCO3-

– 内因子 Intrinsic factor

• pH 0.9-1.5

黏液 - 碳酸氢盐屏障 Mucus-HCO3- barrier

幽门螺旋杆菌 (Helicobacter Pylori)

胰液分泌Pancreatic secretion

• 胰液– pH 7.8~8.4– ~1500 ml/day– Isosmotic – Components:

• Pancreatic digestive enzymes: secreted by pancreatic acini

• Sodium bicarbonate: secreted by small ductules and larger ducts

At low magnification

At higher magnification

• Secretion of pancreatic digestive enzymes– Carbohydrates -- Pancreatic amylase– Pancreatic lipase– Fat Cholesterol esterase– Phospholipase– Trypsinogen– Proteins Chymotrypsinogen– Procarboxypolypeptidase– Proelastase

急性胰腺炎Acute pancreatitis

Acute pancreatitis

胆汁分泌Secretion of bile by the liver

• 胆汁的成分– HCO3

-

– Bile salts

– Phospholipids

– Cholesterol

– Bile pigments

– …

• 胆汁的功能：– Emulsifying or detergent function of bile salts

– Bile salts help in the absorption of:

• Fatty acid

• Monoglycerides

• Cholesterol

• Other lipids

Bile salts and phospholipids convert large fat globules into smaller pieces with polar surfaces that inhibit reaggregation.

Emulsified fat globules are small enough that lipase enzymes gain access todegrade triglyceridesto monoglycerides andfatty acids, which enterthe absorptive cells by simple diffusion or aggregate to form loosely held micelles, which readily break down.

Big Droplets of Fat

Small Droplets of Fat

Micelles

Fatty Acids andMonoglycerides

Chylomicron Assembly

Distribution and Processing

Preventing the cholesterol precipitation & gallstones

Patients with bile duct cancer most often become symptomatic when the cancer obstructs (blocks) the drainage of bile. Because bile cannot be excreted into the bowel, the bilirubin pigments accumulate in the blood, causing jaundice (yellowing of the skin and the whites of the eyes) in 90% of patients. The jaundice is usually associated with itching of the skin (also called "pruritus"). The body compensates partially and excretes some of this bilirubin via the urine, so patients may have dark (cola colored) urine. Because bile cannot reach the intestine, the patient's stools become white (clay colored).

Cholecystitis

大肠的功能• 吸收水分和无机盐• 吸收微生物合成的维生素 B 复合物和维生

素 K• 完成对食物残渣的加工，形成并暂时储存

粪便

In the large intestine, active transport of sodium, coupled with osmotic absorption of water, are the primary activities. Microbes here are active in the production of vitamin K.

排便反射 Defecation reflex

体 温Body Temperature

体 温• 恒温动物保持正常的体温是机体进行新陈

代谢和生命活动的必要条件• 核心温度 Core temperature • 表层温度 Shell temperature

Normal core temperature

Site Mean value of temperature Standard deviation Range of variation of temperature

Axillary 36.79oC 0.357 36.0-37.4 oC

Oral 37.19 oC 0.249 36.7-37.7 oC

Rectal 37.47 oC 0.251 36.9-37.9 oC

The circadian (“about a day”) rhythm of body temperature persists even among patients in a coma; in addition to this basic rhythm, fevers, exercise, and other activities can alter the body temperature.

Body temperature is a controlled variable that is subject to homeostatic regulation.

This cartoon indicates some of the ways that environmental factors can increase or decrease body temperature.

体温调节

• 自主性体温调节 Autonomic

thermoregulation• 行为性体温调节 Behavioral thermoregulation

体温中枢——主要在下丘脑 Hypothalamus

Starting from the upper left, infections, microbial toxins, and other macrophage activators stimulate the production of pyrogenic cytokines. These, in turn, gain access to the circulation and interact with specific receptors (each cytokine has its own receptor) on the hypothalamic endothelium. In addition, microbial toxins can directly trigger receptors on the same endothelium in the hypothalamus and these receptors are also specific for each class of toxins. The response of the hypothalamic endothelium to either cytokines or toxins is the same, that is, the production of prostaglandin E2. Cyclic AMP is released by PGE2 and acts as a neurotransmitter. Elevated cAMP raises the set-point and triggers peripheral heat conservation and production.

Pathways of fever production

肾脏生理学Renal Physiology

肾脏的功能• 调节水和电解质平衡，调节体液渗透压• 调节酸碱平衡• 排出机体代谢终产物及进入体内的过剩物质和

异物• 糖异生• 内分泌：

– 促红细胞生成素（ erythropoeitin ）– 肾素（ renin ）– 1,25- 二羟胆骨化醇（ 1,25-OH2-D3 ）– 其他：激肽，前列腺素（ PGE2, PGI2 ）

尿生成的三个基本过程• 滤过 Filtration• 重吸收 Reabsorption• 分泌 Secretion

Substance X is filtered and secreted but not reabsorbed.

Substance Y is filtered and some of it is reabsorbed.

Substance Z is filtered and completely reabsorbed.

Composition in the Filtration Fluid

Structure of the Filtration Membrane

葡萄糖的重吸收• 正常情况下，全部重吸收• 小管葡萄糖最大转运率 Tm-G:

– Tubular transport maximum for glucose

• 肾糖阈 Renal threshold for glucose– Critical value of the plasma glucose concentration

when the kidney begins to excrete glucose– 160-180 mg/dL

尿量• 正常： 1000-2000ml/24hr• 多尿 Polyuria ： >2500ml/24hr• 少尿 Oliguria ： <400ml/24hr ，或 <17ml/hr• 无尿 Anuria ： <100ml/24hr ，或 12hr 完全

无尿

抗利尿激素Antidiuretic hormone (ADH)

• 又称血管升压素 Vasopressin• 下丘脑合成• 垂体后叶释放• 作用：

– 促进远曲小管和集合管对水的通透性– 收缩血管

Action of antidiuretic hormone on aquaporin (AQP) transport. AC, adenylate cyclase; AP1, transcription factor; AVP, arginine vasopressin; cAMP, cyclic adenosine monophosphate; CRE, cAMP response element; CREB-P, CRE binding protein; EP3, prostaglandin receptor; PGE2, prostaglandin E2. (From Brown D, Nielsen S: The cell biology of vasopressin action. In Brenner BM [ed]: Brenner and Rector‘s The Kidney, 7th ed. Philadelphia, WB Saunders, 2004, p 574.)

水利尿 Water diuresis尿崩症 Diabetes insipidus

In a kidney-failure patient undergoing dialysis, the blood is briefly removed from the body to be circulated through a dialyzer, where dialysis fluid and blood move in counter current directions to remove nitrogenous and other wastes and adjust osmolarity before the blood is returned to the body.

血液透析 Hemodialysis

腹膜透析 Peritoneal dialysis